MINNEAPOLIS (WCCO) — The confirmed number of people sick with E. coli has now jumped to 37 in Oregon and Washington State. State health officials say each of those people had one common experience — they ate at one of eight Chipotle restaurants in the past two weeks.

In response, the Mexican chain has closed 43 locations on the West Coast “out of an abundance of caution.” State investigators haven’t yet pinpointed an exact cause of the outbreak, but say it could be tied to some of kind of produce.

So, how does E. coli get into our food? Good Question.

E. coli is a bacteria that lives in the intestines of humans and animals. Most types of E. coli are harmless, but some can cause diarrhea and, in rare serious cases, kidney failures or even death.

“The way it gets into our food is because feces that are contaminated with E. coli somehow are getting into our food,” said Dr. Craig Hedberg, a professor at the University of Minnesota School of Public Health.

It can find its way to our food through a variety of sources, including meats and vegetables.

For example, E. coli can be found in ground beef following the processing of the meat, so the CDC always recommends always cooking any meat well.

“When you convert a cow into hamburgers, it’s a messy process,” Dr. Hedberg said. “When cattle come into a plant, they may have dried manure of their hide.”

E. coli can also found on various types of produce. Often times, the water source used to irrigate the crops gets infected with E. coli bacteria. In 2011, deer feces were found to be the source of an E. coli outbreak in strawberry fields in Oregon. In that case, one person was killed and 14 others got sick.

Dr. Hedberg recommends always washing vegetables, but says that won’t get rid of all of the E. coli that may be attached to produce.

“What we’ve found is some of this bacteria have to ability to adhere to produce tissues and sometimes they can get into the interior structure of the plant, so no amount of washing is going to get rid of bacteria that is inside the tissues of the plant itself,” he said.

E. coli can also be spread from person to person, but that would be found mostly in daycare settings where children come into constant contact with dirty diapers and dirty hands.

It can also be spread from a person’s hands to food, so handwashing is always recommended.

“If I work in a restaurant and my job is to make a salad and I’m infected with this bacteria and I don’t wash my hands well with soap and water, when I go to make the salad, I’m going to be washing my hands in the salad,” said Dr. Hedberg.

E. coli is estimated to affect 100,000 people in the U.S. every year, compared to an estimated one million people infected with salmonella.

“Salmonella is much more complex than E. coli,” said Dr. Hedberg. “There are many more different types of animals that can carry it, it can survive in the environment and people can also be a source for transmission.”

Heather Brown